This application relates to the manufacture of disposable thermometers, and more particularly to the manufacture of disposable thermometers in which the change of state of a temperature sensitive substance identifies a temperature range of a test specimen.
More specifically, this application relates to a method and apparatus for manufacturing disposable thermometers wherein liquid crystal material is the temperature sensitive substance.
Disposable thermometers which use liquid crystal material as a temperature sensitive substance are known, per se. An example of such a thermometer is found in U.S. Pat. No. 3,633,425. Economics, however, dictate a need for commercial production of such thermometers.
Applicant has found that certain types of reciprocating injector units, of the type commonly used in connection with die-printing operations, would be suitable for applying the liquid crystal material to the thermometers. This makes production of the thermometers by means of such injector units commercially feasible.
A problem connected with the use of such injector units is the fact that the injector units include parts which contain hydrocarbons which are soluble in liquid crystal material, particularly in the rubber gasket between the injector plate and the die plate. Hydrocarbons tend to contaminate liquid crystal material and render it unsuitable for use in a disposable thermometer. It is therefore essential that injector units which are used to deliver liquid crystal material for use in a disposable thermometer be free of materials in which hydrocarbons or other substances which might tend to contaminate the liquid crystal material are soluble.